This invention relates to a controllable illumination device which consists of an illumination matrix with a backlight of primary light sources and a controllable light modulator, whereby an imaging matrix projects the light of said light modulator in bundles through a reproduction matrix, which it permeates full with light, on to at least one viewer. The reproduction matrix can be a stereoscopic or holographic display which contains monoscopic or stereoscopic information. The primary light sources may be point shaped light sources, line shaped light sources or area shaped light sources with at least one light-emitting element per light source.
Displays for 2D representations typically comprise a so-called backlight which illuminates the reproduction matrix. The backlight must have a homogeneously bright surface area which is at least as large as that of the reproduction matrix in order to achieve uniform image brightness. In contrast, with autostereoscopic 3D displays (ASD) for stereoscopic viewing the reproduction matrix must also be illuminated homogeneously, but not the viewing space. Here, different perspective views of the reconstructed object are projected separately into neighbouring regions of the viewing space such that the left and right eyes of the viewer see different views of the object, the viewer thus perceiving a three-dimensional reconstruction. An imaging matrix with periodically arranged cylindrical lenses is therefore often illuminated through line light sources in order to achieve this directed irradiation.
If one or several viewers move, their position changes are preferably detected and the corresponding views are tracked accordingly so that the stereo impression is maintained for that viewer/those viewers. For this, the distance and/or position of the light sources may be variable. A variable arrangement of line shaped light sources in order to be able track a visibility region is also required if instead of the autostereoscopic display a holographic display is used as reproduction matrix. This applies in particular if a holographic display with tracked viewing windows is used as disclosed by the applicant in DE 103 53 439.
The large-area backlight, which is typically used in directed illumination devices, is usually combined for intensity control with a LCD panel, which acts as a shutter, as described by the applicant in OS 103 39 076 A1. This shutter consists of a regular arrangement of controllable transparent and absorbing areas, which only let the light emitted by the large-area backlight pass at the desired positions. The transparent areas are displaced in a suitable manner in order to be able to track the perspective views as described above. For this, the transparent rows or columns on the shutter are controlled accordingly. The largest portion of the light is absorbed by the less or not transparent areas of the shutter. Very powerful backlights are required to achieve sufficient image brightness despite this absorption of large portions of light. Such powerful backlights are expensive as regards both purchase costs and energy consumption. Moreover, the absorbed light considerably heats up the display. Further, the diffused light of a shutter leads to a reduced stereo contrast.
Another device for focussing light on to viewers' eyes in space is disclosed in WO 03/053072. It employs a backlight which can be positioned three-dimensionally. Several configurations are described. The light sources which can be activated in the 3D backlight are projected on to viewers' eyes by an imaging system and tracked according to the viewers' motion. Thereby, on its way to the viewer the light permeates a reproduction matrix, which alternately provides images for the left and right eye of the viewer(s). The disadvantage of this method is the great depth of the autostereoscopic display caused by the three-dimensional backlight and an imaging lens which has an extremely large diameter. In order to confine aberrations of such large lenses outside the optical axis, a sufficiently large focal length must be chosen, which makes the appliance very deep. Moreover, the device is very heavy and a backlight which can be positioned three-dimensionally is difficult to manufacture.
Further, monoscopic and autostereoscopic display illumination systems which use holograms to generate directed light instead of controllable shutter masks are known. WO 02/12930 A1 describes an illumination system which consists of a collimated backlight and two holograms disposed one behind the other. This spatially interleaved double hologram generates a left and a right visibility region for one viewer. The pitch of the interleaved holograms is defined by the pitch of the information display and fixed in the recording process. However, this illumination system is thus not controllable as would be required for tracking the visibility regions, for example if the viewer moves sideways. A re-encoding of the holograms, as would be necessary to be able to track the visibility regions, does not take place.
The illumination system described in WO 00/43841 consists of a light source and a multitude of holograms disposed one behind another. These holograms are controllable in so far as they can be switched between an active condition, where the impinging light is diffracted, to a passive condition without any diffraction effects. The generation of a variable light source pattern by way of re-encoding the holograms is not subject of that invention.
Further, GB 2 404 991 A describes the use of a controllable holographic optical element (HOE) in conjunction with a reflective illumination arrangement. The optical path of an information display is thereby divided into two separate visibility regions. In this way, together with the non-directed backlight for transmissive illumination of the information display, switching between a 2D mode and a 3D mode becomes possible.
Further, above-mentioned devices and methods which employ holograms do not affect the primary illumination system, but always modify the entire light emitted by the backlight. The drawbacks of great power consumption and heating-up are thus not eliminated.